A firewall is a network security device designed to monitor, filter, and control incoming and outgoing traffic based on predefined security rules. Firewalls act as a barrier between trusted internal networks and untrusted external networks, such as the internet.
Firewalls can operate at multiple layers of the OSI model and may inspect packet headers, session states, and even application-level data. Modern firewalls often include advanced features such as intrusion prevention, deep packet inspection, and threat intelligence integration.
Servers and endpoints generate or consume traffic but do not filter it by default. Ethernet is a networking standard, not a device. Firewalls are a foundational security control recommended by virtually all cybersecurity frameworks, including NIST and CIS Critical Security Controls.
By enforcing traffic filtering rules, firewalls help prevent unauthorized access, reduce attack surfaces, and protect systems from threats such as malware, scanning, and exploitation.
